This invention relates to an air-drying paint composition for use in coating steel construction, bridges, buildings, cars, machinery and other substrates for protective and/or decorative purposes.
Heretofore, alkyd and acrylic modified alkyd type paints have been widely used as one-pot, air-drying paints. For reasons of avoiding atmospheric pollution and saving natural resources, it has become a social problem today to decrease the amount of solvent discharged to the atmosphere from coating compositions by providing high solids paints having excellent air-drying capability, workability and film properties without unduly increasing the viscosity thereof. Unfortunately, such requirements are often incompatible. For example, high solids, low viscosity paints may be formulated by employing relatively low molecular weight resins and highly active solvents. The use of low molecular weight resins results in prolonged air-drying time and also decrease in film properties such as hardness, solvent resistance and chemical resistance, while the use of highly active solvents increases production costs and often causes lifting phenomena when two or more coats are overlaid. For systems using low cost solvents such as mineral spirit, it is necessary to use alkyd resins having a greater oil length. However, such systems exhibit poor air-drying capability and, therefore, are not capable of applying in two coats within a day during winter.
Japanese Laid Open (Kokai) Patent Application No. 199777/84 discloses an air-drying paint composition comprising an alkyd resin having an oil length greater than 50% and a nonaqueous dispersion of polymer. Although this system is more advantageous than conventional systems free of such nonaqueous dispersion of polymer, it is not entirely satisfactory in respect of viscosity, air-drying capability, film properties including film gloss and workability. Particularly solvents which are more polar than xylene, such as mineral spirit, cannot be used in this system because polymer particles dispersed in the nonaqueous medium become swollen or dissolved.
It is, therefore, an object of the present invention to provide an air-drying paint which is high solids while retaining a low viscosity, and exhibits an excellent air-drying capability even with the use of a relatively high-boiling point, low-volatile solvent such as mineral spirit as well as a good workability and excellent film properties in hardness, water resistance, solvent resistance, chemical resistance, weatherability and the like.
It is another object of the present invention to provide an air-drying paint of the above type which provides a greater film thickness per coat than is possible by conventional paints.
Other objects and advantages of the present invention will be apparent to those skilled in the art as the description proceeds.